Packaging machines of this type have the advantage that the cross sealing, with which a filled bag is closed off and with which the bottom seam is created for the next bag, occurs during the unwinding movement of the foil tube, so that the time needed for unwinding can be utilized for the sealing task. The time of manufacture can thus be reduced per bag in comparison with those packaging machines where the cross sealing occurs during the time that the foil tube is stationary.
In a known packaging machine of the mentioned type (German AS No. 21 26 498), the foil tube is advanced by the welding jaws and the unwinding movement is not continuous, since a certain time interval passes following the release of the cross sealing jaws from the tube which have produced the cross sealing seams and the engagement of the next following cross sealing jaws. The star-shaped sealing jaw carriers are in the known packaging machine supported on swingable arms. By swinging the arms, the cross sealing jaws approach the foil tube and clamp it. Upon a further rotation of the sealing jaw carriers, the thin sheet material tube is unwound. It is necessary for this downward movement that the two axes of the sealing jaw carriers are moved relative to one another. The sealing jaw carriers and the sealing jaws arranged thereon are necessarily heavy, so that substantial forces due to inertia are created, which limits the operating speed. Also the intermittent unwinding of the thin sheet material tube influences the operating speed.
In a further known packaging machine (U.S. Pat. No. 3,522,689), which is constructed similarly to the afore-described machine according to German AS No. 21 26 498, a total of six sealing jaws are arranged on each sealing jaw carrier, so that a sealing jaw pair can engage the thin sheet material foil before the preceding sealing jaws have freed the foil tube. This results in a continuous unwinding of the foil, however, the bag length cannot be changed, if the continuous unwinding is to be maintained. If the bag length would be doubled by using only three the six jaws of each sealing jaw carrier, then a continuous unwinding would no longer be possible.
Cross sealing jaws rotate about stationary axes in a further known packaging machine (German Pat. No. 31 41 431). Friction segments, with which the foil tube is unwound and which are fixedly connected to the holders for the cross sealing jaws, rotate also about the same axes. A space for filling in the fill material is provided between the leading friction segments and the following cross sealing jaws. The very short welding time is disadvantageous in this packaging machine. Also the characteristic of movement of the cross sealing jaws is such that these first rest only with edges on the thin sheet material foil. The short welding time limits the use of the known machine to a few thin sheet materials of a specific composition. Due to the initial, only linelike contact between the cross sealing jaws and the thin sheet material tube, there exists the danger that the thin sheet material is overheated. A wedge, into which fill material can fall, exists during the closing movement of the cross sealing jaws between the welding surfaces of the two cross sealing jaws, so that the sealing is enhanced. A problem is in this known machine also the arrangement of knives for cutting off the finished bags. The bag sizes can be varied only within narrow limits.
Finally, a packaging machine for packaging of individual pieces is also known in which the foil tube is moved horizontally (German Pat. No. 27 01 443). Welding and cutting jaws are moved on circular tracks in a welding and cutting station. The jaws are shifted only parallel to themselves on the circular tracks, so that their welding surfaces always face the foil tube. This is achieved with the help of carriages, which can be moved perpendicularly to one another and of which one cooperates with an eccentric. The parallel movement of the jaws achieves an advantageous contacting of the jaws on the foil tube, however, only relatively short welding times can be realized at a given speed of movement of the foil tube.
The basic purpose of the invention is to provide a packaging machine of the abovementioned type, as it is known from German AS No. 21 26 498 and U.S. Pat. No. 3,522,689 such that a continuous movement of the thin sheet material is possible and the bag lengths can be chosen as desired. Furthermore, the invention provides a method which with the inventive machine can achieve a particularly high performance.
The first part of the purpose of the invention is attained by providing movable thin sheet material conveyors for unwinding the thin sheet material foil continuously. The conveyors are in the form of unwinding rollers or unwinding belts, which in the area below the forming shoulder rest with frictional resistance on the thin sheet material, and by the relationship between the peripheral speed of the thin sheet material conveyors and the sealing jaw carriers being adjustable, whereby the speed of movement of the sealing jaws during their contact with the foil tube is approximately the same or is less than the peripheral speed of the thin sheet material conveyors.
The unwinding in a so constructed packaging machine does not occur, as this is the case in the known machines, with the sealing jaws (socalled unwinding by tongs), but by means of special thin sheet material conveyors, as they are known in tubular bag packaging machines. By separating the thin sheet material transport and cross sealing, a continuous thin sheet material unwinding can also be maintained when the bag lengths are varied, since it is not necessary like in the known machine according to U.S. Pat. No. 3,522,689 that two cross sealing jaw pairs simultaneously engage the foil tube. Different bag lengths can also be manufactured when the sealing jaw carriers move with an approximately constant angular speed. A bulging out of the lower end of the foil tube occurs then during the manufacture of longer bags. However, it is also possible and technically nonproblematic to substantially vary the angular speed during the movement of the sealing jaw carriers. The peripheral speed of the sealing jaw carriers is then during the manufacture of relatively long bags chosen relatively low in a phase between two cross sealings. When manufacturing relatively short bags, the peripheral speed of the sealing jaw carriers is chosen relatively high between two cross sealings. This avoids an excessive bulging out of the tube end. A small bulging, however, is advantageous for the filling of the bag.
A preferred embodiment of the invention is characterized by the mentioned axes being arranged stationarily, by the sealing jaw holders being radially movable in the sealing jaw carriers and by each sealing jaw holder having two guide elements, each of which being guided on a guideway of a guideway pair, whereby the guideways are closed within themselves and both guideways have the same shape, however, are moved parallel to one another and the cross sealing, at least in the area of the sealing zone in which the cross sealing jaws extend rectilinarly in unwinding direction of the thin sheet material tube, are oriented perpendicularly with respect to the thin sheet material tube.
In a so constructed packaging machine there occur even at a high operating speed only relatively small forces due to inertia, since not all sealing jaw carriers are moved discontinuously, but only the jaw holders carry out relatively small movements relative to the sealing jaw carriers. The special design of the jaw holders assures that the cross sealing jaws come into contact from the start with their entire heating surfaces with the thin sheet material. Burning of the thin sheet material is safely avoided in this manner. The sealing time can extend approximately over a full operating cycle, so that also at a high cycle number a long sealing time is available and in this manner practically all common thin sheet materials can be processed.
A third guideway is advantageously provided which is concentric to one of the mentioned guideways, whereby one of the guideways, which are concentric to one another, is arranged so that one is located on each side of the sealing jaw holders. This results in a strong rigidity of the arrangement even if the sealing jaws are constructed relatively long.
Each sealing jaw carrier has advantageously a shaft and two guide parts. The jaw holders can be suspended particularly advantageously therewith. Advantageous is also the separation of the guideways for the radial movement of the jaw holders and for their rotation. Large guide surfaces for the radial guiding can thus be created.
The construction of the guideways as grooves is advantageous, since in this manner a forced guiding is achieved. However, in principle it is also possible to press the guide elements through spring forces on a guideway.
The jaw holders can be guided particularly advantageously if one guideway is arranged on one side and another guideway on the other side of the sealing jaw carrier. When three guideways are provided, it is particularly advantageous to arrange these concentric guideways so that they cooperate with guide rollers which are both concentric to the swivel axis of the jaw holder. The jaw holder is, in this manner, held particularly advantageously.
The shape of the guideways can be calculated particularly easily if one guide element is concentric to the swivel axis of the associated jaw holder. The shape of the guideways can then be chosen for example advantageously.
One single sealing jaw is principally sufficient for each sealing jaw carrier. Particularly advantageous, however, is the arrangement of two cross sealing jaws on one sealing jaw carrier. Also more than two cross sealing jaws can be provided on one sealing jaw carrier.
The sealing jaw carriers are, according to a further development, supported resiliently flexibly relative to one another. A specific pressure of the cross sealing jaws against one another can be adjusted by the resilient flexibility, which results in a good adjustment to the respective structure of the thin sheet material.
Because of the long contact time of the sealing jaws with the thin sheet material, the arrangement of a knife in the sealing jaws is possible also without any problems. To return the knife, a return spring is provided.
In order to further increase the operating speed, air nozzles for cooling air for cooling off the sealing seam are provided, according to a further development of the invention, on each cross sealing jaw. With this the seam can be cooled off quickly and thus the seam solidifies quickly. The air supply to the nozzles occurs advantageously by an even air distribution system, with which means, aside from the aforesaid even air distribution system, the rate of air flow can be determined.
It is possible in principle that the rotary speed of the shafts of the sealing jaw carriers and the unwinding speed of the foil tube are constant and are at a specific relationship to one another. The relatively small speed variations, which the cross sealing jaws experience in this case in the area of the sealing station, can easily be absorbed by the tube, especially since same is bulged out by the fill material. However, it is also possible to make speed adjustments which can be advantageous particularly during the manufacture of large bags.
The second part of the purpose of the invention is attained by the thin sheet material foil being unwound with a speed which is only little less than the speed of movement (speed of the material) of the material to be packaged relative to the lower end of the fill pipe.
The highest possible performance of the machine is achieved by approximating the unwinding speed for the thin sheet material with the falling speed of the material to be packaged. The material to be packaged is protected in the best possible manner, since a hitting of the material on the bottom of the bag is avoided. This also has the advantage that the bottom seam of the bag to be filled is not stressed, so that a filling is possible prior to the seam of the bag becoming rigid due to cooling off. This substantially contributes to achieving a high operating speed. One can also imagine the inventive method such that packaging portions are enclosed in the bag during their fall. A stress of the bag during filling does not at all take place any longer at an approximation, which is as close as possible to the ideal condition. However, to avoid as much as possible that filler is welded into the cross seams, it is advantageous to maintain a certain difference between material speed and unwinding speed.